The BL Lac Object 1ES 1426+428 , at a red-shift of z = 0.129 , has been monitored by the C at telescope from February 1998 to June 2000 .
The accumulation of 26 hours of observations shows a \gamma -ray signal of 321 events above 250 \ > \mathrm { GeV } at 5.2 standard deviations , determined using data analysis cuts adapted to a weak , steep-spectrum source .
The source emission has an average flux of { \Phi } _ { \mathrm { diff } } ( { 400 \ > \mathrm { GeV } } ) = 6.73 \pm 1.27 ^ { \mathrm { stat } } \pm 1. % 45 ^ { \mathrm { syst } } \times 10 ^ { -11 } \ > \mathrm { cm ^ { -2 } \ > s ^ { -1 } TeV ^ { -1 } } , and a very steep spectrum , with a differential spectral index of \gamma = -3.60 \pm 0.57 which can be refined to \gamma = -3.66 \pm 0.41 using a higher flux data subset .
If , as expected from its broad-band properties , the Very High Energy emission is hard at the source , these observations support a strong absorption effect of \gamma -rays by the Intergalactic Infrared field .